Method and apparatus for interfacing analog telephone apparatus to a digital, analog or hybrid telephone switching system

ABSTRACT

An adaptive handset interface method and apparatus for interfacing a two-wire analog telephone instrument, such as a modem, fax modem, facsimile machine or teleconferencing device, to a digital, analog or hybrid telephone system, such as a private branch exchange (PBX). The interface device is suitable for use with a variety of PBX&#39;s produced by different manufacturers, despite differences in signalling characteristics between the PBX and an associated PBX-compatible telephone. In a preferred embodiment, the invention does not require access to a handset port of a PBX-compatible telephone. The interface device is connected to the extension line along with a PBX-compatible telephone. An analog telephone instrument is then connected to the interface device. In order to communicate with the PBX using a communication protocol appropriate to the PBX, the interface device “learns” the characteristics of the PBX. This is accomplished by: determining whether the telephone system is an analog or digital telephone system; and, if the telephone system is a digital telephone system, monitoring communications between the PBX and the PBX-compatible telephone. Then, the interface device is configured according to the appropriate protocol by retrieving set of operational parameters from a plurality of such sets pre-stored in a memory device within the interface device. The learning technique allows the interface device to automatically adapt itself to variations in signalling characteristics between the PBX and PBX-compatible telephone sets among the different PBX manufacturers.

This application claims the benefit of U.S. Provisional Application No.60/064,382, filed Nov. 6, 1997. This application is acontinuation-in-part of U.S. application Ser. No. 08/625,398, filed Mar.27, 1996, the contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to the field of telephony. More particularly, theinvention relates to an adaptive interface for interfacing a two-wire ora four-wire analog telephone instrument to a digital, analog or hybridtelephone switching system.

BACKGROUND OF THE INVENTION

A two-wire analog telephone set of the type commonly found in the homesof telephone service subscribers typically includes a base unitconnected to a central office of a telephone service provider via abi-directional, two-wire, telephone line and also includes a handsetconnected to the telephone base unit via a four-wire handset cable. Thehandset cable has four wires because, for two-way voice communication,the handset includes both a microphone and a speaker, each of whichrequires a pair of wires. Typically, the telephone base supplies audiosignals to the speaker and a DC biasing voltage to the microphone, whilethe telephone base receives audio signals from the microphone. Atwo-wire to four-wire converter included in the telephone base unitconverts the two central office signals into the four handset signals.In addition, the telephone set includes a ring detector for detecting anAC ring signal provided by the central office and a hook-switch forsignalling the central office for answering or placing calls. When thehandset is removed from its cradle, the hook switch controls draw of DCcurrent from the central office by the telephone set which is detectedby the central office.

A conventional modem transmits digital data over a two-wire telephoneline by modulating an analog carrier signal according to the digitaldata. Typically, the digital data is generated by a computer orfacsimile machine connected to the modem. The carrier signal is a tonewithin the frequency range of telephone transmission line. Uponreception by a second modem at the other end of the transmission line,the digital data is reconstructed by demodulating the received signal.

Business organizations often utilize a telephone switching system forproviding telephone service to telephone users within the organization.The telephone switching system can have an all-digital interface withits corresponding compatible telephone sets, such as in a digitalprivate branch exchange (PBX). Alternately, the telephone switchingsystem can have an all-analog interface, such as is provided by ananalog line card in a PBX or by a central office. In addition, thetelephone switching system can provide a combined digital and analoginterface with its corresponding compatible telephone sets, such as in ahybrid PBX or a key telephone system (KTS). For the purposes of thisdocument, the term “PBX” is utilized to encompass equipment similar tothose the above-listed types of telephone switching equipment.

Telephone sets that are compatible with a particular PBX utilized by abusiness organization are located on the desks of the users. EachPBX-compatible telephone set is connected to the PBX via a correspondingextension line, while the PBX is connected to a telephone serviceprovider via one or more outside lines. The PBX typically includescapability for appropriately connecting incoming calls to the usertelephone sets and for connecting outgoing calls from the user telephonesets to an outside line. In this way, fewer than one outside line pertelephone set is needed, thus, reducing the cost of the telephoneservice. In addition, the PBX typically provides a variety of featuresto the users of the PBX, such as connecting calls among the users andproviding voicemail services.

To implement all of the functions of the PBX, certain control andoverhead communications must take place between each user's telephoneset and the PBX. These communications typically include digital status,initialization and command signals in addition to the two-way voicesignals necessary to carry on a telephone conversation. For example, thePBX must know whether a telephone set is connected to a particularextension line in order to know whether or not to route calls to thatextension. As another example, the PBX must interact with the usertelephone sets in order for the users to receive incoming calls,initiate outgoing calls, terminate telephone calls and to accessvoicemail and other features of the PBX.

In general, communication protocols utilized for control and overheadcommunications differ among the various manufacturers of PBX's. Inaddition, in an all-digital PBX, the voice signals are communicatedbetween the telephone sets and the PBX as digital samples. Thus, analogvoice signals are digitally sampled and encoded according to variousdifferent schemes (e.g. μ-law or A-law) before they are communicated.Upon reception, the digital samples are decoded and converted back intoanalog voice signals. In a hybrid system, voice signals are communicatedas analog signals, while control and overhead communications are digitalsignals. Therefore, a two-wire analog telephone instrument, such as amodem, fax modem, facsimile machine or teleconferencing device, cannotgenerally interface directly with a PBX. Nor can a four-wire analogtelephone instrument, such as a headset, handset or modem, generallyinterface directly with a PBX.

This creates a problem for users of a PBX who wish to use universallyavailable analog telephone instruments, such as modems, fax modems,facsimile machines, teleconferencing devices, headsets or handsets, inaddition to their PBX-compatible telephone sets. This problem hasintensified by the recent increase in demand for access to the worldwide web, which is typically accessed through use of a modem connectedto a personal computer. A proposal has been to provide a dedicatedoutside line for each such analog telephone instrument. This solution isnot entirely satisfactory, however, because it negates the savings whichresult from the PBX limiting the number of required outside lines.Another solution has been to provide an analog line card in the PBX anda separate line connecting the two-wire analog telephone instrument tothe PBX. This solution can be costly due to the need to install separateextension lines to connect each of the PBX-compatible telephone set andthe analog telephone instrument to the PBX.

Another solution has been to provide a device which interfaces a modemwith a telephone set through the handset port of the telephone set. Forexample, U.S. Pat. No. 4,907,267 discloses a modem interface device foruse with a telephone set having a base unit and a handset. The telephoneset can be a two-wire telephone set or a telephone set designed for usewith a PBX. To use the modem interface device, the handset is unpluggedfrom the handset jack of the base and plugged into a handset jack in oneend of the device. Extending from the device is a four-wire cable whichis connected to the handset jack of the base. The device also includes amodular jack for accepting a two-wire cable which connects the device toa two-wire telephone instrument, such as a modem. A series of switchesare manually positioned to select between voice and data communicationsand to configure the interface device to match the signallingcharacteristics of the particular telephone set being used.

The manually operable switch arrangement described in U.S. Pat. No.4,907,267 is improved upon in two products manufactured by UnlimitedSystems Corp. of San Diego, Calif. A first of these products, the“KONEXX Office Konnector,” connects to the base of a telephone set andto the handset to provide an interface for a two-wire telephone,facsimile machine or modem. The device detects when the two-wiretelephone, facsimile machine or modem is placed off-hook for switchingbetween voice and data communications. A second of these products, the“KONEXX Konference,” is similarly connected between the base andhandset, but provides an interface for a teleconferencing device. Foreach of these devices, a manually operable switch is positioned in oneof four positions for adjusting the device to the signallingcharacteristics of the particular telephone set being used.

The aforementioned interface devices, however, can be inconvenient forinterfacing an analog telephone instrument to a PBX. This is because toinstall such an interface device, the handset cord of a PBX-compatibletelephone set must first be disconnected from its base. Then, theinterface device must be connected to both the handset and to the base.Next, the analog telephone instrument must be connected to the interfacedevice. Finally, the switch positions for the interface device must becorrectly set.

Perhaps a more significant drawback, however, is that each time theanalog telephone instrument is used to answer or place a call, the usermust manually place the PBX-compatible telephone set off-hook. This isgenerally accomplished by removing the handset of the PBX-compatibletelephone from its cradle. Similarly, when finished using the analogtelephone instrument, the user must return the PBX-compatible telephoneto its on-hook condition. Otherwise, if the user forgets to return thePBX-compatible telephone to its on-hook condition, incoming calls cannotbe connected and will receive a busy indication. In addition, thehandset port of the PBX-compatible telephone generally does not providea ring signal which may be required for automatic answering functions.Another drawback is that some PBX-compatible telephones do not acceptDTMF signals through the handset port though DTMF signals may berequired by the PBX system for dialing telephone numbers. Thus, forexample, auto-dialing features of an analog device will fail to operate.Therefore, the actual telephone keypad must be used to dial for theanalog device. Furthermore, the cables required for connecting such aninterface device can become tangled and tend to provide a clutteredappearance on the user's desk.

Therefore, what is needed is a technique for interfacing an analogtelephone instrument to a PBX that does not require access to thehandset port of a PBX-compatible telephone. What is further needed issuch a technique that has sufficient flexibility to adapt to thesignalling characteristics of a wide variety of commercially availablePBX's. What is still further needed is such a technique that requires aminimum of additional cables to accomplish its functions and thatminimizes technical ability required from a user.

SUMMARY OF THE INVENTION

The invention is an adaptive interface method and apparatus forinterfacing a two-wire analog telephone instrument, such as a modem, faxmodem, facsimile machine or teleconferencing device, or a four-wireanalog telephone instrument, such as a headset, a handset or a modem, toa private branch exchange (PBX). For purposes of this document, the term“analog telephone instrument” will be used to refer to both two-wire andfour wire telephone instruments. The interface device according to thepresent invention is suitable for use with a variety of PBX's producedby different manufacturers, despite differences in signallingcharacteristics between the PBX and an associated PBX-compatibletelephone. In a preferred embodiment, the invention does not requireaccess to a handset port of the PBX-compatible telephone.

A PBX is generally connected to an associated PBX-compatible telephonevia a two-wire telephone extension line. An extension line for a hybridtelephone switching system, however, can include up to eight wires. In afirst embodiment of the present invention, both the interface device andthe PBX-compatible telephone set are connected to the extension line. Ananalog telephone instrument is then connected to the interface device.The PBX-compatible telephone communicates with the PBX so as to notifythe PBX that the extension line is capable of receiving incoming calls.In addition, the PBX-compatible telephone can initiate and receivetelephone calls without interference by the interface device.

The analog telephone instrument can also initiate and receive telephonecalls. To initiate an outgoing telephone call originated by the analogtelephone instrument, the interface device detects a current draw (adial tone request) by the analog telephone instrument, as occurs whenthe analog telephone instrument goes off-hook. Accordingly, theinterface device emulates a central office from the perspective of theanalog telephone instrument. In response to detecting the analogtelephone instrument going off-hook, the interface device communicatesan appropriate instruction to the PBX so as to emulate thePBX-compatible telephone going off-hook. This is accomplished withouthaving to manually take the PBX-compatible telephone off-hook. Accordingto the first embodiment, a telephone number to be called is dialed byusing a keypad located on the interface device.

To receive an incoming call using the analog telephone instrument, theinterface device receives a notification of the incoming call which issent by the PBX and intended for the PBX-compatible telephone connectedto the corresponding extension line. If the analog telephone instrumentthen goes off-hook, the interface device responds by communicating anappropriate instruction to the PBX so as to emulate the PBX-compatibletelephone going off-hook. This is also accomplished without having tomanually take the PBX-compatible telephone off-hook.

Once a telephone call is connected to the analog telephone instrumentvia the interface device, the interface device provides a two-waycommunication path between the analog telephone instrument and the PBXfor voice or modem signals. Thus, the interface device receives voice ormodem signals from the analog telephone instrument and converts theminto a form suitable for reception by the PBX and receives voice ormodem signals from the PBX and converts them into a form suitable forreception by the analog telephone instrument. For example, if the PBX isan all-digital PBX, the interface device performs appropriateanalog-to-digital and digital-to-analog conversions.

When an incoming or outgoing telephone call is complete, the interfacedevice detects that current is no longer drawn by the analog telephoneinstrument, as occurs when the analog telephone instrument is returnedto its on-hook condition. In response, the interface device communicatesan appropriate instruction to the PBX so as to emulate thePBX-compatible telephone returning to an on-hook condition.

A second embodiment differs from the first embodiment in that the keypadlocated on the PBX-compatible telephone is utilized to dial a telephonenumber to be called. According to the second embodiment, a keypad neednot be provided on the interface device.

A third embodiment differs from the first and second embodiments in thata keypad located on the analog telephone instrument can be utilized todial a telephone number to be called. The interface device receivesdual-tone, multi-frequency (DTMF) signals which are generated by theanalog telephone device as the telephone number is dialed. The interfacedevice then converts these signals into a format appropriate for thePBX.

A fourth embodiment differs from the other embodiments in that theinterface device communicates with the PBX so as to notify the PBX thatthe telephone connected to the extension line is capable of receivingincoming calls. Similar to the third embodiment, the keypad located onthe analog telephone instrument can be utilized to dial a telephonenumber to be called. Thus, in the fourth embodiment, a PBX-compatibletelephone is not required to be connected to the extension line alongwith the interface device.

In order to communicate voice and overhead signals with the PBX using acommunication protocol appropriate to the PBX, the interface device must“learn” the characteristics of the PBX. Therefore, when the interfacedevice is coupled to the PBX, a learning technique is performed.

A first step of the learning technique requires that the interfacedevice determine whether or not the telephone system to which it isconnected communicates voice signals as digital samples, such as anall-digital PBX, or whether the telephone system communicates voicesignals in analog form, such as a hybrid PBX, a KTS, or a central officeof a telephone service provider. The primary functions of the telephonesets compatible with each of these types of telephone switching systemsare powered directly by the associated telephone switching system. Theinventor has observed that the power supply characteristics differ foreach type of telephone switching system relative to the modularinterface terminal locations and the effective DC source resistances.Accordingly, a determination is made by the interface device polling upto eight terminals coupled to the extension line. By discovering whichof the polled terminals are active, the interface device distinguishesbetween hybrid telephone switching systems and other types of telephoneswitching systems. Assuming the telephone switching system is a hybridsystem, the particular model or manufacturer can generally be identifiedby discovering which polled terminals are active.

Assuming the telephone switching system is not a hybrid system, up tothree DC source resistance measurements are taken for the extension linevia the active terminals. A first measurement is an unloaded DCmeasurement. For the second two measurements, the extension line isloaded by alternate fixed resistive loads. The interface compares theresults of these measurements to pre-stored values to determine whetherthe telephone switching system is an all-digital system or an analogsystem.

If the system communicates voice signals in a multi-wire hybrid-typeformat, the interface device configures itself accordingly. Thus, a nextstep in the learning technique is to emulate an off-hook condition. Inresponse to the emulated off-hook condition, the hybrid PBX provides adial tone signal to the receive lines of the extension. The interfacedevice detects the dial tone signal and performs level adjustments forboth the receive and transmit signal paths. The receive signal path isconfigured using the dial tone signal and the transmit path isconfigured using a set of prestored parameters appropriate to the hybridPBX. This is accomplished by the interface device selecting a stored setof operational parameters from a plurality of such sets.

If the system communicates voice signals in an analog format, theinterface device also configures itself accordingly. Thus, a next stepin the learning technique is to emulate an off-hook condition. Inresponse to the emulated off-hook condition, the PBX analog line card orcentral office provides a dial tone signal to the interface device. Theinterface device detects the dial tone signal and performs leveladjustments for both the receive and transmit signal paths. The receivepath is configured using the dial tone signal and transmit path isconfigured by implementing Transmit Objective Loudness Rating (TOLR)sensitivity levels.

Otherwise, if the system communicates voice signals as digital samples,a next step in the learning technique is to determine the signallingprotocol which is utilized for communicating between the PBX and theassociated PBX-compatible telephones. This is accomplished by theinterface device momentarily open-circuiting the extension line. Then,the interface device monitors signals communicated between the PBX andthe PBX-compatible compatible telephone which initialize thePBX-compatible telephone and which notify the PBX that thePBX-compatible telephone connected to the extension line is capable ofreceiving incoming calls.

Then, based upon this determination, the interface device configuresitself according to the appropriate signalling protocol. This isaccomplished by the interface device selecting a stored set ofoperational parameters from a plurality of such sets. The sets ofoperational parameters are pre-stored in a memory device within theinterface device. A selected set of operational parameters configuresthe interface device to communicate with the PBX using a protocolappropriate to the particular PBX being utilized.

Thus, the learning technique allows the interface device toautomatically adapt itself to variations in signalling characteristicsbetween the PBX and PBX-compatible telephone sets among the differentPBX manufacturers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block schematic diagram of an interface deviceaccording to the present invention coupled to a PBX, to a PBX-compatibletelephone set and to one or more analog telephone instruments.

FIG. 2 illustrates a block schematic diagram of the interface controlportion of the interface device according to the present invention.

FIG. 3 illustrates a flow diagram of a learning algorithm according tothe present invention.

FIG. 4 illustrates a schematic diagram of a circuit for measuring asource resistance of the extension lines according to the presentinvention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 illustrates a block schematic diagram of an interface device 100according to the present invention coupled to a telephone switchingsystem (PBX) 102, to a PBX-compatible telephone set 104, to a two-wireanalog telephone instrument 106 and to a four-wire analog telephoneinstrument 108. The telephone switching system 102 can be an all-digitalprivate branch exchange (PBX), a hybrid PBX, a key telephone system(KTS) or a direct line from a central office 110. For the purposes ofthis document, the term “PBX” encompasses all of the above-listed typesof telephone switching equipment. And, for the purposes of thisdocument, the term “PBX-compatible telephone set” refers to a telephoneset 104 specifically designed to interface directly with a particularPBX 102. Typically, the PBX 102 and PBX-compatible telephone set 104 areprovided by the same manufacturer. Though several manufacturers producePBX's and corresponding PBX-compatible telephone sets, a PBX-compatibletelephone set provided by a manufacturer is generally not capable ofinterfacing with a PBX provided by a different manufacturer.

The PBX 102 is coupled to a central office 110 of a telephone serviceprovider via one or more outside lines 112 and is also coupled to a PBXport 114 of the interface device 100 via a extension line 116 and a walljack 118. The extension line 116 is a two-wire line for most types oftelephone switching systems, however, the extension line 116 for ahybrid switching system can include up to eight wires.

As an example, the PBX 102 can be centrally located at a business site,such as in a service room or basement. Several extension lines (only oneis shown—extension line 116) extend to corresponding wall jacks (onlyone is shown—wall jack 118). The wall jacks are typically distributedthroughout the business site. The wall jacks can be located in users'offices, conference rooms and reception areas. Conventionally, thePBX-compatible telephone set 104 would be plugged into the wall jack118. According to the present invention, however, the interface device100 is plugged into the wall jack 118, while the PBX compatibletelephone set 104 is plugged into the interface device 100.

The interface device 100 includes an interface control portion 120 whichis coupled to the PBX 102 via the PBX port 114. Internal to theinterface device 100, the PBX port 114 is coupled to the interfacecontrol portion 120 and to a first terminal of a switch SW1. A secondterminal of the switch SW1 is coupled to a PBX phone port 122. Theswitch SW1 is coupled to be controlled by the interface control portion120. Also internally to the interface device 100, the interface controlportion 120 is coupled to a two-wire analog phone port 124 and to afour-wire analog phone port 126.

Externally to the interface device 100, the PBX-compatible telephone set104 is plugged into the PBX phone port 122, the two-wire analogtelephone instrument 106 is plugged into the two-wire port 124 and thefour-wire analog telephone instrument 108 is plugged into the four-wireport 126. In certain embodiments of the present invention, it is notnecessary for the PBX-compatible telephone set 104 to always be presentto obtain the advantages of the present invention. In addition, it isnot necessary that both telephone instruments 106, 108 be present toobtain the advantages of the present invention.

The telephone instruments 106, 108 can each be a modem, fax modem,facsimile machine, teleconferencing device, headset, handset or othertype of conventional analog telephone instrument. The four-wiretelephone instrument 108 differs from the two-wire telephone instrument106 primarily in that the four-wire telephone instrument 108 transmitsanalog signals via a first pair of wires and receives analog signals viaa second pair of wires (uni-directional signaling), whereas, thetwo-wire telephone instrument 106 communicates analog signals in bothdirections (transmit and receive) via a single pair of wires(bi-directional signaling).

FIG. 2 illustrates a block schematic diagram of the interface controlportion 120 of the interface device 100 illustrated in FIG. 1. A centraloffice emulator 200 is coupled to the two-wire port 124 (FIG. 1). Thecentral office emulator 200 provides DC power to the port 124 anddetects the on-hook/off-hook condition of the two-wire analog telephoneinstrument 106 (FIG. 1) depending upon whether it draws current from thecentral office emulator 200. The central office emulator 200 provides anindication of the on-hook/off-hook condition of the two-wire analogtelephone instrument 106 to a hook switch block 202.

The central office emulator 200 is also coupled to a two-to-four wireconverter 204. Internally to the central office emulator 200, signalsfrom the two-wire port 124 are routed to the two-to-four wire converter204. The two-to-four wire converter 204 can be a conventional circuit,commonly known as a hybrid circuit, which converts the bi-directionalsignals from the two-wire port 124 into separate transmit and receivesignals. These separate transmit and receive signals from thetwo-to-four wire converter 204 are coupled to a TX/RX audio block 206.

The signals from the four-wire port 126 (FIG. 1) are also routed to theTX/RX audio block 206. Two-to-four wire conversion is not required forthese signals because they are already separated into transmit andreceive channels. An indication of the on-hook/off-hook status for thefour-wire telephone instrument can be provided by a user interface (notshown), such as a on/off switch, coupled to the hook switch block 202.

The TX/RX audio block 206 performs appropriate level adjustments forboth the receive and transmit signal paths. Thus, the TX/RX audio block206 includes analog signal processing circuits, such asgain-controllable amplifiers. The RX/TX audio block 206 ensures that thelevels of the voice or modem signals received from the PBX 102 (FIG. 1)are adjusted for compatibility with the analog telephone instrument 106or 108 (FIG. 1) and ensures that the levels of the signals received fromthe analog telephone instrument 106 or 108 are adjusted forcompatibility with the PBX 102.

Via the TX/RX audio block 206, the separate transmit and receive signalsfrom the two-to-four wire converter 204 and from the four-wire port 126are coupled to a pulse code modulation (PCM) encoder/decoder (CODEC)block 208 and to an analog line interface block 210. Preferably, the PCMCODEC block 208 is selectively active or inactive depending upon whetherthe PBX 102 (FIG. 1) communicates voice or modem signals over theextension line 116 (FIG. 1) as digital samples or whether the PBX 102communicates these signals in analog format. If the PBX 102 communicatesthese signals as digital samples, then the PCM CODEC block 208 isactive. Conversely, if the PBX 102 communicates these signals in analogformat, then the CODEC block 208 is inactive.

Assuming the PCM CODEC block 208 is active, a digital line transceiver212 and digital line interface 214 are also active. The PCM CODEC block208 converts analog voice or modem signals received from the TX/RX audioblock 206 into a serial digital data stream. Preferably, this conversionis preformed according to A-LAW or μ-LAW companding techniques. Theserial data stream formed by the PCM CODEC block 208 is representativeof the voice or modem signal received from the analog telephoneinstrument 106 or 108 and is provided to the digital line transceiver212.

The digital line transceiver 212 then combines the digitally sampledvoice or modem signals with any necessary overhead or command signals,thereby forming a combined serial data stream. For example, the hookswitch block 202 notifies the digital line transceiver 212 of theon-hook/off-hook status of the telephone instrument 106 or 108 (FIG. 1).The digital line transceiver 212 responds by including an appropriatecommand to the PBX 102 in the combined serial data stream.

The combined serial data stream formed by the digital line transceiver212 is then provided to the digital line interface block 214. Thedigital line interface block 214 communicates the combined serial datastream to the PBX via a learning block 216. The digital line interface214 is preferably controlled by the learning block 216.

Because the combined serial data stream is received by the PBX 102 (FIG.1), it must be in a format that is compatible with, and understandableby, the particular PBX 102 coupled to the interface device 100. Forexample, the data must be appropriately synchronized with the PBX 102and must be appropriately compressed and encoded according to therequirements of the PBX 102. In addition, the command and overheadinformation included in the combined serial data stream must berecognizable to the PBX 102.

The specific parameters required for appropriately forming the combinedserial data stream, however, generally vary among the variousmanufacturers of PBX's. Therefore, the PCM CODEC block 208 and digitalline transceiver 212 are preferably pre-configured to performanalog-to-digital conversion appropriately for the particular PBX 102coupled to the interface device 100. In addition, the digital lineinterface 214 is also pre-configured to form the combined serial datastream appropriately for the particular PBX 102 coupled to the interfacedevice 100. This pre-configuration of the PCM CODEC 208, digital linetransceiver 212 and digital line interface 214 is performed undercontrol of the learning block 216 and according to data stored inmanufacturer specific protocol sets 218.

The digital line interface 214 receives a serial stream of digital datagenerated by the PBX 102 and provides this serial data stream to thedigital line transceiver 212. The digital line transceiver 212 thenappropriately separates overhead and commands from voice or modemsignals and passes the voice or modem signals to the PCM CODEC 208 fordecoding. To perform this function appropriately, the digital linetransceiver 212 is pre-configured, under control of the learning block214 according to data stored in the manufacturer specific protocolsblock 218.

As an example of operation of the digital line transceiver 212, if thePBX 102 indicates that an incoming telephone call is to be connected tothe extension line 116, the digital line transceiver 212 recognizes thiscondition and, in response, communicates this condition to an incomingcall detect block 220. The incoming call detect block 220 then notifiesthe PCM CODEC block 208 to prepare to receive digital samples from thedigital line transceiver 212. The incoming call detect block 220 canalso notify the central office emulator 200 to send a ring signal to thetwo-wire analog telephone instrument 106 (FIG. 1).

Then, when the two-wire analog telephone instrument 106 goes off-hook,the central office emulator 200 (FIG. 2) recognizes this condition and,in response, notifies the hook switch block 202. Alternately, a manualswitch notifies the hook switch block when the four-wire analogtelephone instrument 108 (FIG. 1) goes off-hook. The hook switch block202 then appropriately notifies the digital line transceiver 212 whichthen communicates with the PBX 102 so as to emulate the PBX-compatibletelephone set 104 going off-hook.

The PCM CODEC block 208 converts the digital samples received from thedigital line transceiver 212 into an analog signal. The digital samplesare received as a one-bit-wide stream of digital values. Accordingly,the conversion is performed by appropriately parsing the received streamof digital values into a series of digital values, each digital valuehaving an appropriate width. Then, any compression and/or encodingperformed by the PBX 102 (FIG. 1) is reversed. Finally, the analogsignal is reconstructed from the series of digital values. To performthis conversion appropriately, the PCM CODEC block 208 ispre-configured, under control of the learning block 216 according to amanufacturer specific format and synchronization of the digital samplesstored in the manufacturer specific protocols block 218.

The manufacturer specific protocol sets 218 includes a plurality of setsof conversion parameters appropriate for PBX's produced by variousdifferent manufacturers. Each set of parameters includes informationrelating to an appropriate format and synchronization of the digitalsamples, decompression and decoding of the digital samples, appropriatecompression and encoding of the analog signals into digital samples,generation of commands to the PBX 102 and recognition of commands fromthe PBX 102. In general, these parameters are specific to each PBXmanufacturer.

The analog signal generated by the PCM CODEC block 208 is provided tothe TX/RX audio block 206 for routing to the two-wire port 124 via thecentral office emulator 200 and to the four-wire port 126.

A line filter 222 is coupled to the digital line interface 214 and tothe analog line interface 210 for obtaining supply power for theinterface device 100 (FIG. 1) from the PBX 102 (FIG. 1) via theextension line 116 (FIG. 1). The interface device 100 can also beexternally powered. The line filter 222 filters frequency componentsabove a predetermined threshold from the extension line 116 therebyforming an unregulated DC voltage. Alternately, an unregulated DCvoltage can be obtained from a battery supply or from a rectified ACline voltage. The unregulated DC voltage is provided to an isolatedswitching power supply 224. The isolated switching power supply 224provides power to the circuits of the interface device 100, but iselectrically isolated from the source of power. When the digital linetransceiver 212 is active, the digital line transceiver 212 preferablyprovides a synchronizing signal to the switching power supply 224. Thissynchronizing signal controls switching of the power supply 224 to occurout of phase with digital-to-analog sampling performed by the PCM CODECblock 208 for minimizing sampling errors caused by switching noise.

Assuming that the PBX 102 communicates voice or modem signals in analogformat, such as when an analog line card is used in the PBX 102 or whenthe PBX 102 is a hybrid switching system, the PCM CODEC block 208 ispreferably inactive. The analog line interface 210 receives analogsignals from the PBX 102 via a bi-directional communication path throughthe learning block 216. The analog line interface block 210 converts thebi-directional signals into separate uni-directional transmit andreceive signal paths. Accordingly, the analog signals are communicatedbetween the analog line interface block 210 and the TX/RX block 206 viaseparate uni-directional signal paths.

Separate uni-directional transmit and receive signal paths connect theTX/RX audio block 206 to the four-wire telephone instrument 108 (FIG.1). For the two-wire telephone instrument 106 (FIG. 1), the two-to-fourwire converter 204 converts the separate uni-directional signal pathscoupled to the TX/RX audio block 206 into a bi-directional signal paththrough the central office emulator 200.

The analog line interface block 210 monitors the signals originated bythe PBX (FIG. 1) for detecting commands from the PBX. For example, theanalog line interface block 210 detects whether an incoming call to isto be connected to the extension line 116. Assuming that the analog lineinterface block 210 detects an incoming call, the analog line interfaceblock 210 notifies the incoming call detect block 220 of this condition.The incoming call detect block 220 then notifies the TX/RX audio block206 to prepare to receive incoming voice signals from the PBX 102 (FIG.1). In response, the incoming call detect block 220 can also notify thecentral office emulator 200 to send a ring signal to the two-wire analogtelephone instrument 106.

The analog line interface block 210 also combines the analog voice ormodem signals received from the TX/RX audio block 206 with any necessaryoverhead or command signals. For example, the hook switch block 202notifies the analog line interface 210 of the on-hook/off-hook status ofthe telephone instrument 106 or 108 (FIG. 1). The analog line interface210 responds by sending an appropriate command to the PBX 102, forexample, by drawing a DC current from the PBX 102.

Note that for a hybrid PBX, the overhead and command signals sent to thePBX 102 may be in the form of serialized or parallel digital data,though the voice or modem signals are communicated in analog format.Generally the overhead and command signals for a hybrid system arecommunicated via separate lines within the extension line 116 (FIG. 1)from the lines utilized for communicating voice signals. As mentioned,when the PBX 102 is hybrid switching system, the voice signals arecommunicated between the PBX 102 and the analog telephone instrument viathe analog line interface 210 and TX/RX audio block 206. For a hybridswitching system, however, a hybrid interface block 226 is provided forcommunicating overhead and command signals with the PBX 102. The hybridinterface block 226 is preferably pre-configured under control of thelearning block 216 and according to data stored in manufacturer specificprotocol sets 218.

As an example of operation of the hybrid interface block 226, when thePBX 102 sends a command that an incoming call is to be directed to theextension line 116, the hybrid interface block 226 notifies the incomingcall detect block 220. Also, when the hook switch block 202 indicates tothe hybrid interface block 226 that the analog telephone instrument 106or 108 (FIG. 1) is off-hook, the hybrid interface block 226 requests adial tone from the PBX 102.

An FSK modem 232 is also coupled to the manufacturer specific protocolsets 218. The FSK modem 232 allows updates, additions, or modificationsto be made to the manufacturer specific protocol sets 218 from a remotelocation over a telephone line connection.

According to a first embodiment of the present invention, a keypad 228and a dual-tone, multi-frequency (DTMF) generator 230 are provided forinitiating telephone calls from the analog telephone instrument 106 or108 (FIG. 1). The keypad 228 is coupled to the DTMF generator 230. TheDTMF generator 230 is coupled to the TX/RX audio block 206 and to thePCM CODEC block 208. For example, to initiate a telephone call, thetwo-wire analog telephone instrument 106 is placed off-hook. Inresponse, the central office emulator 200 notifies the hook switch block202 of this condition. The hook switch block 202 then notifies theanalog line interface 210, the digital line transceiver 212 and thehybrid line interface 226. An active one of the analog line interface210 or the digital line transceiver 212 then sends an appropriatecommand to the PBX 102 (FIG. 1) so as to emulate the PBX-compatibletelephone set 104 (FIG. 1) going off-hook. Once the PBX recognizes thatcall is to be initiated, the keypad 228 is utilized to dial thetelephone number to be called. The DTMF generator 230 then generatesdual tones for each digit of a telephone number dialed via the keypad228.

In an alternate embodiment, the keypad 228 is replaced with a voicerecognition block which converts a user's voice commands into signalsappropriate for controlling the DTMF generator block 230. Such anembodiment could be utilized, for example, so that the user's handsremain free to perform other tasks, or could be utilized by personshaving limited use of their hands.

The dual tones are then provided by the DTMF generator 230 to the TX/RXaudio block 206 and to the PCM CODEC block 208. Assuming that the PBX102 is has an analog interface, the dual tones are passed to the PBX 102through the analog line interface 210 and learning block 216. Otherwise,assuming the PCM CODEC block 208 is active, the dual tones are convertedaccording to the protocol required for the particular PBX 102 (FIG. 1)being utilized. Accordingly, the PCM CODEC block 208 is pre-configuredfor this conversion under control of the learning block 216 andaccording to data stored in manufacturer specific protocol sets 218. Theappropriately converted dual tones are then passed to the PBX 102 viathe digital line transceiver 212, the digital line interface 214 and thelearning block 216.

A second embodiment differs from the first embodiment in that the keypadlocated on the PBX-compatible telephone set 104 (FIG. 1) is utilized todial a telephone number to be called. According to the secondembodiment, therefore, the keypad 228 (FIG. 2) and DTMF generator (FIG.2) 230 need not be provided.

A third embodiment differs from the first and second embodiments in thata keypad located on the analog telephone instrument 106 or 108 (FIG. 2)can be utilized to dial a telephone number to be called. The interfacedevice 100 (FIG. 1) receives dual-tone, multi-frequency (DTMF) signalswhich are generated by the analog telephone device 106 or 108 (FIG. 1)as the telephone number is dialed. An active one of the TX/RX audioblock 206 (FIG. 2) or PCM CODEC 208 (FIG. 2) then converts these signalsinto a format appropriate for the PBX 102 (FIG. 1).

A fourth embodiment differs from the other embodiments in that theinterface device 100 (FIG. 1) communicates with the PBX 102 (FIG. 1) soas to notify the PBX 102 that the extension line 116 (FIG. 1) is capableof receiving incoming calls. A keypad located on the analog telephoneinstrument 106 or 108 (FIG. 1) or the keypad 226 (FIG. 2) can beutilized to dial a telephone number to be called. Thus, in the fourthembodiment, a PBX-compatible telephone set 104 (FIG. 1) is not requiredto be connected to the extension line 116 along with the interfacedevice 100 (FIG. 1). In this embodiment, however, a PBX-compatibletelephone set 104 is required for appropriately configuring theinterface device 100. Once the interface device 100 is appropriatelyconfigured, the PBX-compatible telephone set 104 can be disconnectedfrom the interface device 100.

When an incoming or outgoing telephone call is complete, the centraloffice emulator 200 (FIG. 2) of the interface device 100 (FIG. 1)detects that current is no longer drawn by the analog telephoneinstrument 106 or 108, as occurs when the analog telephone instrument106 or 108 is returned to its on-hook condition. In response, thecentral office emulator 200 (FIG. 2) recognizes this condition andnotifies the hook switch block 202 (FIG. 2). The hook switch block 202then notifies an active one of the digital line transceiver 212 oranalog line interface 210, which then communicates with the PBX 102 soas to emulate the PBX-compatible telephone set 104 returning to itson-hook condition.

In order to appropriately configure the interface device 100 (FIG. 1),particularly the PCM CODEC block 208, the digital line transceiver 212,the TX/RX audio block 206, the hybrid line interface 226 and the analogline interface block 210 to communicate with the PBX 102 (FIG. 1)according to a communication protocol appropriate to the particular PBX102 being utilized, the interface device 100 must “learn” thecharacteristics of the PBX 102. To accomplish this, the interface device100 performs a learning algorithm.

FIG. 3 illustrates a flow diagram of a learning algorithm which controlsoperation of the learning block 216 (FIG. 2) according to the presentinvention. The learning algorithm is initiated for appropriatelyconfiguring the interface device 100 (FIG. 1). Thus, logic circuitryincluded in the learning block 216 perform the function of determiningwhether the telephone switching system 102 communicates voice signals asdigital samples or in analog format. In addition, logic circuitryincluded in the learning block 216, in conduction with data stored inthe manufacturer specific protocol sets 218 (FIG. 2), perform thefunctions of identifying a communication protocol utilized by thetelephone switching system 102 and configuring the interface device 100according to the protocol. It will be apparent, however, that amicroprocessor or controller circuit operating according to a storedsoftware program could also perform these same functions.

As an example, the learning algorithm determines which one or ones ofthe digital line interface block 214, the analog line interface block210 and the hybrid line interface block 226 is to be active. Thelearning algorithm can be initiated each time power is supplied to theinterface device 100. Alternately, the learning algorithm is initiatedeach time a reset control input is applied to the learning block 216(FIG. 2). For example, the control input can be in response to a userpressing a button on the interface device 100.

Upon initiation, the learning algorithm moves from a state 300 to astate 302. Preferably, the learning algorithm determines whether or notthe PBX 102 (FIG. 1) to which the interface device 100 (FIG. 1) isconnected communicates voice signals as digital samples, such as anall-digital PBX, or whether the telephone system communicates voicesignals in analog form, such as a hybrid PBX or a KTS. Note that acentral office of a telephone service provider also communicates voicesignals in analog form. Thus, assuming the interface device 100 isconnected directly to a central office 110 (FIG. 1) of a telephoneservice provider, rather than to a PBX 102 (FIG. 1), the learningalgorithm appropriately configures the interface device 100.

The inventor has observed that the power supply characteristics of theextension lines 116 (FIG. 1) differ for each of these types of telephoneswitching systems relative to the modular interface terminal locationsand the effective DC source resistances as measured via the PBX port 114(FIG. 1). For example, a hybrid switching system generally has moreactive wires in the extension lines 116 than does either an analog lineinterface to a PBX or an all-digital interface to a PBX. In addition, aDC source resistance for an analog interface tends to be higher than aDC source resistance for an all-digital interface.

Accordingly, in the state 302, the interface device polls up to eightterminals of the port 114. This is accomplished by measuring a voltageacross selected pairs of the wires included in the extension line 116via the PBX port 114 (FIG. 1). By discovering which of the polledterminals are active, the interface device 100 (FIG. 1) distinguishesbetween hybrid telephone switching systems and other types of telephoneswitching systems. Assuming the PBX 102 is a hybrid system, theparticular model or manufacturer can generally be identified bydiscovering which polled terminals are active.

Once the step of polling is complete, the learning algorithm moves fromthe state 302 to the state 304. Based upon the results of the pollingperformed in the state 302, the learning algorithm determines whether ornot the PBX is a hybrid PBX.

Assuming that the switching system communicates according to amulti-wire hybrid-type format, the learning algorithm moves from thestate 304 to a state 306. In the state 306, the interface device 100emulates an off-hook condition. Then, the learning algorithm moves fromthe state 306 to a state 308. In response to the emulated off-hookcondition, the hybrid PBX is expected to provide a dial tone signal tothe receive wires of the extension line 116. If the interface device 100does not detect the dial tone signal in the state 308, this indicatesthat an erroneous measurement was performed in the state 302. Therefore,the learning algorithm returns from the state 308 to the state 302 wherethe measurements are repeated. If the interface device 100 is notappropriately configured after a predetermined number of attempts, thenthe interface device 100 preferably indicates an error condition.

Assuming the interface device 100 detects the dial tone signal in thestate 308, the interface device 100 moves to a state 310. In the state310, the interface device 100 configures itself for a hybrid interfaceby performing level adjustments for both the receive and transmit signalpaths through the TX/RX audio block 206 (FIG. 2). The receive signalpath is configured using the dial tone signal and the transmit signalpath is configured according to a selected set of parameters appropriateto the hybrid PBX from the manufacturer specific protocol sets 218. Thisappropriately configures the interface device 100 for providing voicecommunication between the PBX 102 (FIG. 1) and analog telephoneinstrument 106 or 108 (FIG. 1). Additionally, in the state 310, thehybrid line interface 226 (FIG. 2) is configured to communicate overheadand commands to the PBX 102 according to parameters stored in themanufacturer specific protocol sets 218. Once the interface device 100has been appropriately configured in the state 310, the learningalgorithm moves to a state 312 which signifies that the learningalgorithm is complete. Also in the state 312, the configurationparameters obtained in the state 310 are stored in non-volatile memory,such as a serial EEPROM, so that they will not be lost in the event of apower failure.

Assuming that in the state 304 it is determined that the PBX 102(FIG. 1) is not a hybrid system, then the learning algorithm moves fromthe state 304 to a state 314. Because the PBX 102 is not a hybrid PBX,the interface to the PBX 102 can be an analog interface, as in the caseof an analog line card or a central office. Alternately the interface tothe PBX 102 can be a digital interface, as in the case of an all-digitalPBX. In either case, the extension line 116 (FIG. 1) is expected toinclude only two active wires.

The inventor has observed that a difference between these types oftelephone systems is in a DC source resistance measured via the twoactive wires of the extension lines 116 (FIG. 1). For example, a centraloffice of a telephone service provider typically provides an unloadedline voltage of 48 volts dc. A source resistance depends upon thedistance to the central office, however, 1300 ohms is typical.All-digital PBX's generally have unloaded line voltages between 14 and48 volts DC with source resistances between 30 and 60 ohms. It can beseen, therefore, that PBX's that communicate voice signals as digitalsamples generally have much lower source resistance than a centraloffice or a PBX that communicates voice signals in analog format.Therefore, the determination of whether or not the PBX 102 (FIG. 1)communicates voice signals as digital samples or in analog form isaccomplished by effectively measuring the DC source resistance.

FIG. 4 illustrates a schematic diagram of a circuit for measuring asource resistance of the extension lines 116 (FIG. 1) according to thepresent invention. A DC voltage, Vsource, is provided by the PBX 102(FIG. 1) via a series resistance Rsource. A DC voltage, Vline, isreceived by the learning block 216 of the interface device 100 (FIG. 1).A switch SW2 selectively coupled one of three resistive loads across theextension lines 116. A first load LOAD1 has a large resistance value(e.g. greater than 20 M ohms or open circuit) so as to leave theextension line essentially unloaded. Second and third loads LOAD2 andLOAD3 have alternate values which are lower than the value of LOAD1 soas to the load the extension lines to varying degrees. For example, thevalue of LOAD2 can be comparable to an expected value of the sourceresistance Rsource for an analog interface (e.g. approximately 1 Kohms), while the value of LOAD3 can be comparable to an expected valueof the source resistance Rsource for an all-digital interface (e.g.approximately 50 ohms), but is preferably a higher resistance to avoidany potentially excessive flow of current.

In the state 314, three DC source resistance measurements are taken forthe extension line 116 (FIG. 1) via the active two terminals of the PBXport 114 (FIG. 1). A first measurement is an unloaded DC measurement.For this measurement, the switch SW2 is coupled to the first resistanceLOAD1 and the resultant level of the voltage Vline is detected.Similarly, for the second measurement, the switch SW2 is coupled to thesecond resistance LOAD2 and the resultant level of the voltage Vline isdetected. For the third measurement, the switch SW2 is coupled to thethird resistance LOAD3 and the resultant level of the voltage Vline isdetected. For each measurement the value of Vline is influenced by therelative values of Rsource and the resistance value coupled to theswitch SW2 by voltage division.

Then the learning algorithm moves from the state 314 to a state 316.Because the results of the measurements taken in the state 314 areindicative of the values of Rsource and Vsource, in the state 316, theinterface device 100 compares the results of these measurements, orratios thereof, to pre-stored values to determine whether the telephoneswitching system is an all-digital system or an analog system.

If the comparison made in the state 316 indicates that the PBX 102(FIG. 1) communicates voice signals as digital samples, a next step inthe learning algorithm is to determine the signalling protocol which isutilized for communicating between the PBX 102 and the associatedPBX-compatible telephone set 104 (FIG. 1). Accordingly, the learningalgorithm moves from the state 316 to a state 318.

In the state 318, the interface device 100 (FIG. 1) momentarilydisconnects the PBX-compatible telephone set 104 (FIG. 1) from theextension line 116 (FIG. 1) by momentarily opening the switch SW1(FIG. 1) and then closing the switch SW1. Then, learning algorithm movesfrom the state 318 to a state 320.

The PBX 102 (FIG. 1) detects that the PBX-compatible telephone set 104has been disconnected and, then, reconnected to the extension lines 116.In response, the PBX 102 communicates with the PBX-compatible telephoneset 104 to initialize the PBX-compatible telephone set 104. Theseinitialization signals differ among the various manufacturers and modelsof PBX's. Therefore, they provide indicia (a “signature”) by which theparticular PBX manufacturer and model can be recognized.

In the state 320, the interface device 100 (FIG. 1) monitors the indiciaprovided by these initialization signals communicated between the PBX102 (FIG. 1) and the PBX-compatible telephone set 104 (FIG. 1) andcompares them to pre-stored indicia. Each pre-stored indicia is storedin the manufacturer specific protocol sets 218 in association with acorresponding one of the sets of parameters utilized for appropriatelyconfiguring the interface device 100 (FIG. 1). Then, the learningalgorithm moves to a state 322. Assuming that the interface device 100recognizes the indicia (the “signature”) provided by the initializationsignals, the interface device 100 configures itself according to theappropriate signalling protocol. Accordingly, the learning algorithmmoves from the state 320 to a state 322.

In the state 322, the learning block 216 selects an appropriate storedset of operational parameters from a plurality of such sets pre-storedin the manufacturer specific protocol sets 218 and appropriatelyconfigures the PCM CODEC 208 and digital line transceiver 212 accordingto the selected set. Then, the learning algorithm moves from the state324 to a state 326.

In the preferred embodiment, once the interface device 100 (FIG. 1) isappropriately configured for the particular PBX 102 (FIG. 1) beingutilized, a verification is performed. Therefore, in the state 326, theinterface device 100 sends a command to the PBX 102 (FIG. 1) whichsimulates the PBX-compatible telephone set 104 (FIG. 1) going off-hook.Then, the learning algorithm moves from the state 326 to a state 328. Inthe state 328, the interface device 100 determines whether the PBX 102is providing a dial tone in response to the command sent in the state324. Assuming a dial tone is detected, the learning algorithm moves tostate 330 which signifies that the learning algorithm is complete. Alsoin the state 330, the protocol and system configuration parameters arepreferably stored in non-volatile memory, such as a serial EEPROM, sothat they will not be lost in the event of a power failure.

Alternately, if in the state 328, a dial tone is not detected, or, if inthe state 322, the interface device 100 does not recognize the indicia(the “signature”) the learning algorithm returns to the state 302, andlearning algorithm begins again. If the interface device 100 is notappropriately configured after a predetermined number of attempts, thenthe interface device 100 preferably indicates an error condition.

Assuming the PBX 102 (FIG. 1) communicates voice signals in an analogformat, the interface device 100 (FIG. 1) configures itself accordingly.Thus, if it is determined in the state 316 that the PBX 102 communicatesvoice signals in an analog format, the learning algorithm moves from thestate 316 to a state 332. In the state 332, the interface device 100emulates an off-hook condition. In the preferred embodiment, this isaccomplished by placing an appropriate resistance across the extensionlines 116 so that the PBX 102 senses a current draw via the extensionlines 116. Then, the learning algorithm moves from the state 332 to astate 334.

In response to the emulated off-hook condition, the PBX 102 (FIG. 1) isexpected to provide a dial tone signal to the extension lines 116 (FIG.1). Accordingly, in the state 334, the interface device 100 determineswhether the dial tone is detected. Assuming that the dial tone isdetected, the learning algorithm moves from the state 334 to a state336.

In the state 336 and based upon the level of the dial tone signal, theinterface device 100 performs level adjustments for both the receive andtransmit signal paths through TX/RX audio block 206 of the interfacedevice 100. The receive path is appropriately configured first utilizingthe dial tone. Then, using side tone characteristics linking the receiveand transmit paths, the transmit path is appropriately configured. Thetransmit path is preferably configured by implementing TransmitObjective Loudness Rating (TOLR) sensitivity levels.

Once the transmit and receive paths have been appropriately configured,the learning algorithm moves to state 338 which signifies that thelearning algorithm is complete. Also in the state 338, the protocol andsystem configuration parameters are preferably stored in non-volatilememory, such as a serial EEPROM, so that they will not be lost in theevent of a power failure.

The present invention has been described in terms of specificembodiments incorporating details to facilitate the understanding of theprinciples of construction and operation of the invention. Suchreference herein to specific embodiments and details thereof is notintended to limit the scope of the claims appended hereto. It will beapparent to those skilled in the art that modifications may be made inthe embodiment chosen for illustration without departing from the spiritand scope of the invention. Specifically, it will be apparent to one ofordinary skill in the art that the method of the present invention couldbe implemented in several different ways and the apparatus disclosedabove is only illustrative of the preferred embodiment of the presentinvention and is in no way a limitation.

What is claimed is:
 1. A method of interfacing an analog telephoneinstrument to a telephone switching system, the method comprising stepsof: a. providing a signal path for communicating signals between theanalog telephone instrument and the telephone switching system; b.identifying a communication protocol utilized by the telephone switchingsystem from among a plurality of communication protocols; and c.configuring the signal path to operate according to the protocol, suchthat if the analog telephone instrument and the telephone switchingsystem operate according a same protocol signals are passed unalteredand if the analog telephone instrument and the telephone switchingsystem operate according different protocols one from the other, thesignals are translated as they are passed between the analog telephoneinstrument and the telephone switching system.
 2. A method ofinterfacing an analog telephone instrument to a telephone switchingsystem, the method comprising steps of: a. providing a signal path forcommunicating signals between the analog telephone instrument and thetelephone switching system; b. identifying a communication protocolutilized by the telephone switching system from among a plurality ofcommunication protocols wherein the step of identifying thecommunication protocol comprises a step of initiating the telephoneswitching system to communicate with a telephone set wherein thetelephone set is pre-configured for compatibility with the telephoneswitching system; and c. configuring the signal path according to theprotocol.
 3. The method according to claim 2 wherein the signal path isutilized for communicating voice and control signals between the analogtelephone instrument and the telephone switching system.
 4. The methodaccording to claim 3 further comprising a step of detecting anon-hook/off-hook condition of the analog telephone instrument.
 5. Themethod according to claim 4 further comprising a step of providing anindication of the on-hook/off-hook condition of the analog telephoneinstrument to the telephone switching system via the signal path inresponse to the analog telephone instrument changing from an on-hookcondition to an off-hook condition.
 6. The method according to claim 4further comprising a step of providing an indication of theon-hook/off-hook condition of the analog telephone instrument to thetelephone switching system via the signal path in response to the analogtelephone instrument changing from an off-hook condition to an on-hookcondition.
 7. The method according to claim 2 wherein the signal pathincludes a converter for converting digital voice samples into an analogsignal.
 8. The method according to claim 1 wherein the step ofinitiating comprises a step of momentarily disconnecting the telephoneset from an extension line coupled to the telephone switching system. 9.The method according to claim 8 wherein the step of identifying furthercomprises a step of monitoring communication between the telephoneswitching system and the telephone set.
 10. The method according toclaim 9 wherein the step of identifying further comprises a step offorming indicia of the communication between the telephone switchingsystem and the telephone set.
 11. The method according to claim 10wherein the step of identifying further comprises a step of comparingthe indicia to a plurality of pre-stored indicia wherein each pre-storedindicia is stored in association with a corresponding set of operationalparameters for configuring the signal path according to a correspondingone of the plurality of communication protocols.
 12. The methodaccording to claim 11 further comprising a step of retrieving a set ofcorresponding parameters when a match is found during the step ofcomparing.
 13. A method of interfacing an analog telephone instrument toa telephone switching system, the method comprising steps of: a.determining whether the telephone switching system communicates voicesignals as digital samples or in analog format wherein the step ofdetermining includes a step of measuring a first voltage supplied by thetelephone switching system to a resistive load; b. activating a firstsignal path through the apparatus when the telephone system communicatesvoice signals as digital samples, the first signal path forcommunicating the voice signals between the analog telephone instrumentand the telephone switching system wherein the first signal pathincludes a converter for converting the digital samples into an analogsignal; and c. activating a second signal path through the apparatuswhen the telephone system communicates voice signals in analog format,the second signal path for communicating the voice signals between theanalog telephone instrument and the telephone switching system whereinthe second signal path includes analog signal processing circuits. 14.The method according to claim 13 further comprising a step of adaptingan active one of the first and second signal paths according torequirements of the telephone switching system.
 15. The method accordingto claim 13 further comprising a step of adapting the second signal pathaccording to requirements of the telephone switching system wherein thestep of adapting comprises a step of adjusting an amplification levelaccording to a level of a dial tone provided by the telephone switchingsystem.
 16. The method according to claim 15 wherein the step ofdetermining further comprises a step of measuring a second voltagesupplied by the telephone switching system under unloaded conditions.17. The method according to claim 16 wherein the step of determiningfurther comprises a step of comparing a ratio of the first and secondvoltages to a range of expected ratios.
 18. The method according toclaim 13 further comprising a step of identifying a communicationprotocol utilized by the telephone switching system.
 19. The methodaccording to claim 18 further comprising a step of detecting anon-hook/off-hook condition of the analog telephone instrument.
 20. Themethod according to claim 19 further comprising a step of providing anindication of the on-hook/off-hook condition of the analog telephoneinstrument to the telephone switching system in accordance with theidentified protocol in response to the analog telephone instrumentchanging from an on-hook condition to an off-hook condition.
 21. Themethod according to claim 19 further comprising a step of providing anindication of the on-hook/off-hook condition of the analog telephoneinstrument to the telephone switching system in accordance with theidentified protocol in response to the analog telephone instrumentchanging from an off-hook condition to an on-hook condition.
 22. Aninterface apparatus for interfacing an analog telephone instrument to atelephone switching system, the interface apparatus comprising: a. afirst port configured for coupling the apparatus to the telephoneswitching system wherein the telephone switching system is a privatetelephone switching system; b. a second port configured for coupling theapparatus to a telephone set wherein the telephone set is pre-configuredfor compatibility with the telephone switching system; c. a third portconfigured for coupling the apparatus to the analog telephoneinstrument; d. a switch for selectively coupling the first port to thesecond port; and e. a control circuit coupled for controlling the switchwherein the control circuit controls the switch to momentarilydisconnect the first port from the second port for initiatingcommunication between the telephone switching system and the telephoneset.
 23. The interface apparatus according to claim 22 wherein thecontrol circuit comprises a first signal path between the first port andthe third port.
 24. The interface apparatus according to claim 23wherein the first signal path includes a converter for convertingdigital samples into an analog signal.
 25. The interface apparatusaccording to claim 24 wherein the telephone switching systemcommunicates voice signals as digital samples.
 26. The interfaceapparatus according to claim 25 wherein the control circuit comprises asecond signal path between the first port and the third port and whereinthe second signal path does not include a converter for converting ananalog signal into digital samples.
 27. The interface apparatusaccording to claim 26 wherein the first signal path is active when thetelephone switching system communicates the voice signals as digitalsamples and wherein the second signal path is active when the telephoneswitching system communicates the voice signals in analog format. 28.The interface apparatus according to claim 26 wherein the controlcircuit detects an on-hook/off-condition of the analog telephoneinstrument and notifies the telephone switching system via an active oneof the first or second signal paths in response to a change in theon-hook/off-hook condition of the analog telephone instrument.
 29. Theinterface apparatus according to claim 22 wherein the control circuitdetects an on-hook/off-condition of the analog telephone instrument andnotifies the telephone switching system in response to a change in theon-hook/off-hook condition of the analog telephone instrument.
 30. Amethod of interfacing an analog telephone instrument to a telephoneswitching system, the method comprising steps of: a. determining whetherthe telephone switching system is a hybrid telephone switching systemwherein the step of determining whether the telephone switching systemis a hybrid telephone switching system comprises a step of monitoring afirst selected pair of wires included in an extension line coupled tothe telephone switching system; b. activating a first signal paththrough the apparatus when the telephone system is a hybrid telephoneswitching system, the first signal path for communicating the voicesignals between the analog telephone instrument and the telephoneswitching system wherein the first signal path includes analog signalprocessing circuits; and c. when the telephone switching system is not ahybrid telephone switching system, determining whether the telephoneswitching system communicates voice signals as digital samples or inanalog format.
 31. The method according to claim 30 further comprising astep of activating a second signal path through the apparatus when thetelephone system communicates voice signals as digital samples, thesecond signal path for communicating the voice signals between theanalog telephone instrument and the telephone switching system whereinthe second signal path includes a converter for converting the digitalsamples into an analog signal.
 32. The method according to claim 30further comprising a step of activating the first signal path when thetelephone switching system communicates voice signals in analog format.33. The method according to claim 32 wherein the step of determiningwhether the telephone switching system is a hybrid telephone switchingsystem comprises a step of monitoring a second selected pair of wiresincluded in the extension line.
 34. The method according to claim 30wherein the step of determining whether the telephone switching systemcommunicates voice signals as digital samples or in analog formatcomprises steps of: a. placing a first load across a selected pair ofwires included in an extension line coupled to the telephone switchingsystem; and b. monitoring a first voltage level across the load.
 35. Themethod according to claim 34 further comprising steps of: a. placing asecond load across the selected pair of wires included in the extensionline; b. monitoring a second voltage level across the load; and c.comparing a ratio of the first voltage and the second voltage to anexpected range of ratios.
 36. An apparatus for interfacing an analogtelephone instrument to a telephone switching system, comprising: a. asignal path for communicating signals between the analog telephoneinstrument and the telephone switching system; b. means for identifyinga communication protocol utilized by the telephone switching system fromamong a plurality of communication protocols; and c. means forconfiguring the signal path according to the protocol, such that if theanalog telephone instrument and the telephone switching system operateaccording a same protocol signals are passed unaltered and if the analogtelephone instrument and the telephone switching system operateaccording different protocols one from the other, the signals aretranslated as they are passed between the analog telephone instrumentand the telephone switching system.